Method and apparatus for the production of magnesium



y H. P. DAVIS 2,349,408

METHOD AND APPARATUS FOR THE PRODUCTION OF MAGNESIUM Filed Feb. 20, 19422 Sheets-Sheet 1 fire-1' I /N\/ENT'OR 1 HARRY/2 DA V/JJDECEAJEQ.

B Y CLAR/TA DA v S, ADM/N/S TAA TR/X.

H. P. DAVIS Mayv 23, 1944.

METHOD AND APPARATUS FOR THE PRODUCTION OF MAGNESIUM 2 Shets-Sheet 2Filed Feb. 20, 1942 Fig. 2

/A/\/E NTOR HARRY f? 04 W5, DECEASED. 5r CL Are/TA DAV/J,ADM/N/JTRATR/X.

FIG. 5.

' Patented May 23', 1944 METHOD AND APPARATI IS FOR THE PRO- DUCTION OFMAGNESIUM Harry P. Davis, Palo Alto, Calif.; Clarita, Davis,administratrix of said Barry P. Davis, deceased,

assignor, by mesne assi California Francisco, tion,

Finance Corporation gnments, to The Anglo National Bank of SanFrancisco, San

Calif., a national banking associaas trustee for the benefit ofReconstruction San Francisco, Calif., a

corporation of the United States Application February 20, 1942, SerialNo. 431,752

3 Claims.

This invention relates to the production of metallic magnesium by the.reduction of magnesium oxide-containing raw material, particularly ofburned dolomite or magnesite, with the aid of a reducing agent such assilicon (ferrosilicon) or aluminum or a mixture of both, or of similarreducing agents which do not generate gaseous products of oxidation.

It is well known that in efiecting the above reduction operation withthe use of a continuously fed furnace, various difficulties areencountered as well in the type in which the operation is effected at atemperature above the melting point of the reaction components, as inthe other type in which the mixture is heated at a temperature below itsmelting point. Both processes are disadvantageous. The reduction ofmagnesia in the liquid state is a rather slow reaction, leaving behind aconsiderable proportion of the unaltered magnesia; moreoverdisengagement of the magnesium vapor from the molten metal mass isdifficult; finally there is an appreciable attack on the furnace liningby the molten slag. On the other .hand reduction exclusively in thesolidstate, while proceeding at a more rapid rate, gives rise todifliculties in removing the spent residue; moreover, seriousdifliculties arise from the fact that in conducting the operation suchas to obtain economical rates of vapor flow, thevapor evolved will carryover dusty impurities 'into the condenser, as'a consequence of whichthere will not be recovered metal answering as to practical purityrequirements.

The art has therefore resorted to intermittent processes. But operationsof this kind have generally the disadvantage of being wearisome. This isin particular the case with magnesium reduction, since it is necessaryto wait before discharging the retort until it cools to a temperaturebelow 80-100 0., since otherwise the magnesium would react with theatmospheric oxygen and nitrogen, which reaction may be so violent thatthe magnesium may be set on fire.

It is the object of the invention to reduce the time required forcarrying out the whole cycle of operation to a minimum, and to enablethereby the operation to be carried out on a very large scale withoutthe use of an excessive amount of retort units. Another object of theinvention is to facilitate the removalof the spent residue from the zoneof the reaction. A further object of the invention is to enable the ma nsium va to be disengaged at a rate high enough for obtainingcommercially economical rates of vapor flow, and yet to produce a soliddeposit practically free from solids carried over by the vapor. I Stillanother object of the invention is to produce higher durability of theapparatus by allowing the exhausted residues to be more easilydischarged.

Other objects and advantages will be apparent from the followingspecification in connection with the accompanying drawings.

Referring to the drawings:

Figure 1 is a vertically longitudinal section through the apparatusembodying my invention;

Figure 2 is a section taken on the line A-A of Figure 1;

Figure 3 is a fragmentary section taken on an enlarged scale, showingdetails of the apparatus;

Figure 4 is a horizontal section showing an alternative embodiment ofthe apparatus;

Figure 5 is a view of details in connection with the briquettes to befed into the apparatus.

Referring first to Figure 1, a relatively long steel cylinder l whichhas a closed bottom, and is equipped with a releasable cover 2 at thehead, and a discharging device 3 with a door 4 at the bottom, forms theouter shell of the apparatus. This outer shell is insulated by arefractory lining 5 impermeable for gases. In the interior of theenclosed vertical shaft 24, which constitutes the retort, there areelectrical heating means 9 and II disposed, whereas in the interior ofthe upper portion there is a condenser E, removably situated which isprovided with acooling device 1. The condenser 6 is split vertically asat 23 into halves, or into three or four sections, so that it can beopened and the condensed material readily removed from its surface. Anysuitable means for evacuating the whole mounting may be connectedthereto by the pipe 8. g

Inside the retort there is centrally displaced a tubular electricresistance heating device 9, resting by supports Ill on the inwardlyinclined wall of the discharge device 3. A larger annular electricheating device I l is disposed on the inside of the refractory lining 5.Within the annular interspace between the outer and the inner centralheating devices there are placed a plurality, for instance 8, of tubularmembers [2, destined for receiving the charge I3, which are providedwith means I 4 adapted to form a substantially unobstructed passagewayfor the vapor released from the charge, and centrally disposed withinthe charge so as to reduce, by displacement, the radial extent thereof.In the case as shown in the drawings, the said central duct membercomprises a tube having round about a large number of perforations fromend to end, thereby permitting the charge l3, which occupies the annularspace between said duct member and the inside wall of the tube, to beuniformly supplied with heat, andv thus also to diseng e magdevice 9 tothe evacuating means being provided thereupon, and all of the Jointsbeing sealed by a sand seal [1 heaped up on the plate l5. At their. openunder ends the tubular heatin device 9 and the charge container tubes l2are sealedby another bottom sand seal it. The object of both these sealsis substantially to prevent the metallic vapor evolved from enteringinto interspaces where they are not wanted, and thus coming into contactwith the heating elements and brickwork. At the upper, ends the chargecontainer tubes l2 are provided with a conical cap or cover l9, which isperforated to form a screen. After the removal of the cover 2 andlifting out the condenser 6, the charge is fed in and is spread by thecones i9 in the open annular space between the duct member H, and theinside wall of the tubes l2, up to a level somewhat below the plat l5.Thereupon condenser i is dropped down into position, cover 2 closed, andvacuum applied through the connection 8 to produce residualpressure'below two millimeters. Heat is now applied by means of theelectric heating elements 9 and II, to maintain the charge at atemperature causing active vaporization below slum; The vapor disengagedescape through the lateral openings of the central duct members I of thecharge container tubes l2, and rises in the condenser 6, where itcondenses as a thick annular deposit of crystalline character adheringto the inner surface. There follow the steps of completely cooling down,sweeping out by agas 'indifferent to magnesium (which is introduced andwithdrawn by suitably positioned pipes not shown in the drawings),opening cover 2, and lifting out the condenser 6 for recovering thesublimate. The bottomcover 4 can now be opened to discharge the bottomsand seal, and thereupon also the spent residues b gravity. Finally thebottom opening is closed by cover 4, and the bottom sand seal rearrangedin its proper place by filling, through the annular space between theduct member I ands-the inside wall of the tubes 12, the material usedfor the purpose.

paratus is now ready for being charged again The "Q1 with the mixture ofmagnesium oxide-containing material, and reducing agent under treatmentlAfter reintroducing the condenser, closing the required, the describedcycle of operationis set going again;

The charge may consist of pellets, tablet or briquets, for instance of(Figure 5) ovoid shape, which are preferably preheated in the compactedstate, to a temperature of 700-900 C., to free them substantiallycompletely from carbon di- 5 the upper portion oxide, and to save timeand energ in the operation of the electric retort furnace.

Materials preferably used for arranging the sand seals are magnesiumoxide or spent residues 5 of the operation, both in very finesubdivision.

l0 ring 22, which interspace is intended to receive the charge. The ductmembers II are disposed, at regular intervals, in the charge itself. Theoperation of this form of the device is apparent from the foregoingdescription:

For effecting reduction with the aid of ferrosilicon. for instance 100parts by weight of burned dolomite, may be mixedmp with 13.8 parts byweight of ferrosilicon. With a vacuum of about 0.1 millimeter, reductiontakes place at about I claim: 1

1. An apparatus for the production of metallic magnesium by reducingmagnesium oxide-containing material with the aid of reducing agents,

capable of exclusively furnishing solid reduction products, comprisingin combination a longitudinally extended receptacle of substantiallytubular shape, closed at the bottom of the lower portion .adapted to beheated toserve as a retort, and

provided with a removable cover at the top of the upper portion adaptedto be kept cool, to serve as a condenser, a removable condenser linerpositioned in the upper portion, sealing means for preventing thepassage of vapor from the heated 5 portion to enter into the interspacebetween the the melting point of magnecondenser liner and the-receptaclewall, a plurality of charge container tubes with vapor .conducting meanscentrally positioned therein, and

causing the vapor to escape through a plurality taining material withthe aid of reducing agents capable of furnishing exclusively solidreduction products, comprising in combination a longitudi p nallyextended receptacle of substantially tubular shape, closed at thevbottom, of the lower portion adapted to be heated to serve as a retort,and

provided with a removabl cover at the top of adapted to be kept cool toserve as a condenser, a removable condenser liner of. the split typepositioned in the upper portion, sealing means for preventing thepassage of vapor from the heated portion to enter into cover 2 andreducing-the pressure to the: extent the interspace between thecondenser liner and the receptacle wall, a plurality of charge containertubes with vapor conducting means centrally positioned therein, andcausing the vapor to escape through a plurality of relatively smallpassageways, which means Open into acommon condenser.

1?. Davis.

